“The Unravelling of Space-Time”

[pood]

In other quantum news, scientists in China create quantum-cat state lasting a record-breaking and eye-popping 1,400 seconds!

The daunting paper is here. Not peer-reviewed.

 

[Jarhyn]

A chaotic system is deterministic and causal, but initial conditions can not be defined enough to predict lomg term outcomes. Local weather is an example.

Chaos can be demonstraed by experiment.

That’s right, but in QM it really is indeterministic. But probabilities can be calculated.

So, it might not be. It is random but not necessarily indeterministic.

How can something be deterministically random?

Well, start off by taking a random finite "shape" of size (radius) 1000, in a "universe" that is going to last 1000 frames (as measured from the center of the shape).

Lets assume this shape has some properties to make it easier to think about namely that it is composed of "voxels", and each "voxel" has a "best guess center of mass/gravity" of the whole at that moment as one of its properties, regardless of whether that individual voxel is empty.

In each frame, frames communicate their idea of where the center of the universe happens to be, and send those messages at a rate of one frame per frame radiating out.

This means that the center of the system will only become aware of the edges of the system at frame 1000 or thereabouts (I may be off by one).

Now, this is fully deterministic, and also completely random, because the center in the next frame is not related to the new information that determines the new center. It's completely unpredictable from prior information.

 

[steve_bank]

As those is a philosophy thread thread we are arguing semantics. Knuth who wrote what used to be a reference text in commuter science back in the 80s said random is a definition. Whatever meets the definition is then random.

A random variable is one where previous events do not affect the next event.

Put 10 balls in a box numbered 0-9, shake and pick one, and put it back. Repeat.

You now have a random number generator. Regardless of the previous occurrence the probability of the next pick is always 1/10. It is easy to demonstrate,number poker chips 0-9 and give a good shake.

Repeat 1000 times and each number will occur about 100 times. A uniform integer random distribution.

A probabilistic system. If there was an algorithm that predicted without fail which number would be picked, that would be deterministic.

Both probabilistic and deterministic are causal.

If I sample random electrical noise in an electronic system I can not predict what the voltage will be. Knowing the distribution I can predict what percentage of the time the voltage will be between two values.

Way back in high school chemistry I was taught there is no such thng as an exact number. There is awys an uncetinty in amesuremnnt.

Way back in physics 101the firt lab was abiut mesuremnts. We had to measure the dimesins of a metal blaock with a micrometer. Tkae multiple readings and average tghe results. Calcuytae standard deviation.

The resultt of the measurent is not exact it is an estmate of the true value.

Point is even withut QM there is still uncertainties.

I get into a car and figure if I drive for 1 hour at 60 miles per hour I will have gone 60 miles. I start a clock and start driivng.

Distance is speed * time, it is deterministic. I stop after 1 hour and read the odometer. Taking into account inaccuracies in the clock and odometer I can say the distance is 60 miles within an experimental error +- x percent.

If I repeat the experiment 1000 times the results will have a statistical distribution. Deterministic but probabilistic. A deterministic equation, but the results are not exactly predictable.